This application relates to a refrigerant system utilizing tandem compressors sharing a common condenser, but having separate evaporators, and wherein an economizer circuit and a reheat coil are incorporated.
Refrigerant systems are utilized in applications to change the temperature and humidity or otherwise condition the environment. In a standard refrigerant system, a compressor delivers a compressed refrigerant to an outdoor heat exchanger, known as a condenser. From the condenser, the refrigerant passes through an expansion device, and then to an indoor heat exchanger, known as an evaporator. In the evaporator, moisture may be removed from the air, and the temperature of air blown over the evaporator coil is lowered. From the evaporator, the refrigerant returns to the compressor. Of course, basic refrigerant systems are utilized in combination with many configuration variations and optional features. However, the above provides a brief understanding of the fundamental concept.
In more advanced refrigerant systems, a capacity of the air conditioning system can be controlled by the employment of so-called tandem compressors. The tandem compressors are normally connected together via common suction and common discharge manifolds. From a single common evaporator, the refrigerant returns through the common suction manifold to each of the tandem compressors. From the individual compressors the refrigerant is delivered into the common discharge manifold and then into a single common condenser. The tandem compressors are also separately controlled and can be started and shut off independently of each other such that one or both compressors may be running at a time. By controlling which compressors are operating, control over the capacity of the entire system is achieved. Often, the two compressors are selected to have different capacities, such that even greater flexibility in capacity control is provided. Also, tandem compressors may have shutoff valves to isolate some of the compressors from the active refrigerant circuit, when they are shutdown. Moreover, if these compressors operate at different suction pressures, then pressure equalization and oil equalization lines are frequently employed.
One advantage of the tandem compressor is that more capacity control is provided, without the requirement of having each of the compressors operating on a dedicated circuit. This reduces the system cost.
However, certain applications require cooling at various temperature levels. For example, in supermarkets, low temperature (refrigeration) cooling can be provided to a refrigeration case by one of the evaporators connected to one compressor and intermediate temperature (perishable) cooling can be supplied by another evaporator connected to another compressor. In another example, a computer room and a conventional room would also require cooling loads provided at different temperature levels, which can be achieved by the proposed multi-temp system as desired. However the cooling at different levels will not work with an application of a standard tandem compressor configuration, as it would require the application of a dedicated circuit for each cooling level. Each circuit in turn must be equipped with a dedicated compressor, dedicated evaporator, dedicated condenser, dedicated expansion device and dedicated evaporator and condenser fans. This arrangement having a dedicated circuitry for each temperature level would be extremely expensive.
In addition, a technique known as an economizer circuit has been utilized in refrigerant systems. The economizer circuit increases the capacity and efficiency of a refrigerant system. To this point, a system having a common condenser communicating with several evaporators has not been utilized in combination with any economizer circuit. Notably, applicants have a co-pending application, filed on even date herewith, entitled “Refrigerant Cycle With Tandem Compressors for Multi-Level Cooling, and assigned Ser. No. 10/975,887.
In some cases, while the system is operating in a cooling mode, the temperature level at which the air is delivered to provide comfort environment in a conditioned space may need to be higher than the temperature that would provide the ideal humidity level. Generally, the lower the temperature of the evaporator coil is the more moisture can be removed from the air stream. These opposite trends have presented challenges to refrigerant system designers. One way to address such challenges is to utilize various schematics incorporating reheat coils. In many cases, a reheat coil placed in the way of an indoor air stream behind the evaporator is employed for the purposes of reheating the air supplied to the conditioned space after it has been cooled in the evaporator, where the moisture has been removed as well.
While reheat coils have been incorporated into air conditioning systems, they have not been utilized in an air conditioning system having an ability to operate at multiple temperature levels by employing tandem compressors, with at least one of the tandem compressors operating in conjunction with the economizer circuit.